1. Technical Field
The present invention relates to a stabilized monomer dispersion containing inorganic oxide nanoparticles and a process for preparing the same. More particularly, the present invention relates to a stabilized monomer dispersion containing inorganic oxide nanoparticles with high refractive index and a process for preparing the same.
2. Description of Related Art
It is well known that some inorganic oxides such as titania (also known as titanium dioxide), zirconia (also known as zirconium dioxide), and ceria (also known as cerium dioxide) exhibit high refractive index. Therefore if such high refractive inorganic oxides were modified with organics, they can be formed into transparent and high refractive optical films and thus increase their utility. Such inorganic dioxides are now briefly discussed as follows.
Titanium dioxide (TiO2), also known as titanium white, exists three crystal forms, namely anatase, rutile, and brookite. Titanium dioxide is a white pigment which has been used in significant amount in most applications. It can also be used as an additive in cosmetic for absorbing ultraviolet light and thus providing sun-screen effect. Among them, the anatase also possesses a photo-catalytic property for rendering deodorization, disinfection, decontamination, and demisting effects.
As to the zirconium dioxide (ZrO2), it is a major oxide of zirconium and is normally a white, odorless, and tasteless crystal and is hardly soluble in water, hydrochloric acid, or dilute sulfuric acid. It exists in the nature as a baddeleyite, which is a monoclinic crystalline structure. Since zirconium dioxide is chemically inactive and has a high melting point, high resistivity, high refractive index, and low thermal expansion coefficient, it is an important high heat-resistant material, insulating ceramic material, and ceramic opacifier.
Cerium dioxide (CeO2) is a white or light yellow solid and is hardly soluble in water or common acids and bases solution. Recently, cerium dioxide powder is of great importance in the catalytic industries, functioning mainly as an oxidative catalyst or as a catalyst support. For example, cerium dioxide can be used in a three-way catalyst (TWC) converter catalyzing the oxidation of carbon monoxide, nitrogen oxides, hydrocarbons, etc. exhausted from vehicles and thereby reduce air pollution caused by such exhaust.
The above-mentioned high refractive inorganic oxides are usually prepared by a sol-gel process, which is a general process of conversion between two physicochemical states. More specifically, the term “sol” refers to colloidal particles which are evenly dispersed in a liquid and remained active therein. The colloidal particles have a particle size ranging from 1 to 100 nm and exhibit Brownian motion while being suspended in the liquid. As to the gel, it is formed by evaporating solvent in the sol continuously to increase the concentration of the colloid particles so that the particles collide with each other and re-combine to form a multi-dimensional cross-linked structure, which molecular weight would be infinitely increased and could be shaped as desired.
In the sol-gel preparation process, the precursor of inorganic oxide (e.g., titanium alkoxide or zirconium alkoxide, etc.,) reacts in an alcohol solvent having the same number of carbon atoms as the alkyl group of the alkoxide in the precursor so as to prevent the alkoxy of the alkoxide from inter-reacting with the alkyl group of the alcohol. Then, condensation and hydrolysis are carried out to form a sol-gel oxide. The sol-gel oxide is subsequently mixed with other materials and subjected to cross-linking after evaporating the solvent to obtain the desired inorganic oxides.
However, such a sol-gel process described above is complicated since an inorganic oxide nano-material must be prepared in advance, and then mixed with other materials to be reacted.
After conducting intensively investigation on the preparation processes of inorganic oxide nanoparticles, the inventors of the present application found that if a dispersion containing stably suspended inorganic oxide nanoparticles can be prepared directly in a reactive monomer, then a polymer material having the desired thermal stability can be easily obtained upon polymerizing the reactive monomer suspended with the inorganic oxide nanoparticles, thus completed the present invention.